The following description of the background of the invention is provided simply as an aid in understanding the invention and is not admitted to describe or constitute prior art to the invention.
C peptide is a peptide that is formed as part of the process of proinsulin conversion (via cleavage) to insulin before release from endocytic vesicles within the pancreas. Human C peptide has a molar mass of about 3020.3 amu.
C peptide binds to receptors at the cell surface and activates signal transduction pathways that result in stimulation of Na+, K+ ATPase and endothelial nitric oxide synthase (eNOS). Both of these enzymes have reduced activities in type 2 diabetes. C peptide also functions in repair of the muscular layer of the arteries.
C peptide levels instead of insulin are often measured in newly diagnosed diabetes patients because insulin concentration in the portal vein can range from two to ten times higher than in the peripheral circulation. The liver extracts about half of the insulin from plasma, but this varies with the nutritional state of the subject. Thus, C peptide may be a more comprehensive indicator of insulin status than direct insulin measurement. Patients with type 1 diabetes are unable to produce insulin efficiently and therefore will have a decreased level of C peptide, while C peptide levels in patients with type 2 diabetes are typically normal or even elevated. Thus, C peptide measurement is used to distinguish type 1 diabetes from type 2 diabetes. Additionally, as C peptide is formed during natural insulin production, measuring C peptide in patients undergoing insulin therapy may help determine how much natural insulin the patient is producing.
C peptide measurement can also be used to determine if a patient may have a gastrinoma associated with Multiple Endocrine Neoplasm syndrome. A significant number of Multiple Endocrine Neoplasm syndromes presenting with gastrinoma also include pancreatic, parathyroid, and pituitary adenomas. Higher levels of C peptide together with the presence of a gastrinoma suggests that organs other than the stomach may harbor a neoplasm. C peptide may also be assessed in patients suspected of insulin abuse, and in women with Polycystic Ovary Syndrome to assess degree of insulin resistance.